This invention relates to apparatus which is used to effect continuous puffing of material such as grain cereals and small cereal dough pieces or pellets and more particularly it has reference to means for feeding into the puffing chamber successive charges of the material.
Under one prior art practice, continuous puffing is produced by an apparatus comprising a pressurized puffing gun or chamber having at its respective ends an orifice open to a relatively low pressure zone and an inlet into which successive charges of the material and a pressurized gaseous fluid are directed by a charging valve. Such a valve includes a movable member, such as a rotor, having at least one passageway extending therethrough in a plane which intersects the axis of the rotor. As the rotor revolves, it repeatedly brings the passageway to a position where it receives a charge of material from a supply hopper and thence into alignment with the inlet and a source of pressurized gaseous fluid, such as steam, so that the charge of material and an amount of fluid are forced into the chamber.
The rotor turns continuously and the material to be puffed flows by gravity down into the passageway which has its two end portions enlarged by at least one sharply diverging wall. In practice, the rotor may, for example, be provided with two passageways which are at right angles to each other, non-intersecting and spaced along the axis of the rotor. Steam is generally used as the pressurized gaseous fluid to drive the charges of material out of the passageways and into the chamber where the steam serves as a processing fluid for the material.
Difficulties arise in the operation of such apparatus because the material to be puffed may have a moisture content, by weight, of 5-20 percent so that the material becomes sticky as soon as it is contacted by the steam. Hence, instead of being discrete particles, the cereal grain or dough pellets form sticky masses which adhere to the rotor and especially to the diverging walls at the end portions of the passageways so that complete discharge of the material from the passageway is prevented. The problem is especially troublesome when rice or cereal dough pellets are being puffed. The longer a charge of material, or any part of it, remains in the passageway, the greater is the problem due to sticky material.
Since the material flows from the supply hopper into the passageway by gravity, the rotor must turn slowly enough to permit a significant charge of material to enter the passageway. The production capacity of the apparatus is therefore largely dependent on the speed of rotation of the rotor. In the operation of the prior art apparatus, small amounts of stray stream may rise upwardly from the valve to the supply hopper and thereby add to the problems caused by sticky material.